No - A visa is not required for travel to Guam

Guam is a United States territory; therefore entry requirements are the same as for the United States of America. For US citizens, no visa is required for travel to Guam.

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Passport Requirements:

U.S. Citizens traveling to and returning directly from a U.S. territory are not considered to have left the United States and do not need to present a passport. If entering a U.S. territory from another country, a valid passport is required.